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Background: Transcatheter renal denervation (RDN) has had inconsistent efficacy and concerns for durability of denervation. We aimed to investigate long-term safety and efficacy of transcatheter microwave RDN in vivo in normotensive sheep in comparison to conventional radiofrequency ablation., Methods and Results: Sheep underwent bilateral RDN, receiving 1 to 2 microwave ablations (maximum power of 80-120 W for 240 s-480 s) and 12 to 16 radiofrequency ablations (180 s-240 s) in the main renal artery in a paired fashion, alternating the side of treatment, euthanized at 2 weeks (acute N=15) or 5.5 months (chronic N=15), and compared with undenervated controls (N=4). Microwave RDN produced substantial circumferential perivascular injury compared with radiofrequency at both 2 weeks [area 239.8 (interquartile range [IQR] 152.0-343.4) mm 2 versus 50.1 (IQR, 32.0-74.6) mm 2 , P <0.001; depth 16.4 (IQR, 13.9-18.9) mm versus 7.5 (IQR, 6.0-8.9) mm P <0.001] and 5.5 months [area 20.0 (IQR, 3.4-31.8) mm 2 versus 5.0 (IQR, 1.4-7.3) mm 2 , P =0.025; depth 5.9 (IQR, 1.9-8.8) mm versus 3.1 (IQR, 1.2-4.1) mm, P =0.005] using mixed models. Renal denervation resulted in significant long-term reductions in viability of renal sympathetic nerves [58.9% reduction with microwave ( P =0.01) and 45% reduction with radiofrequency ( P =0.017)] and median cortical norepinephrine levels [71% reduction with microwave ( P <0.001) and 72.9% reduction with radiofrequency ( P <0.001)] at 5.5 months compared with undenervated controls., Conclusions: Transcatheter microwave RDN produces deep circumferential perivascular ablations without significant arterial injury to provide effective and durable RDN at 5.5 months compared with radiofrequency RDN.

Objectives: This study sought to develop a method to assess renal sympathetic nerve function through localization and pacing of aorticorenal ganglia (ARG)., Background: Transcatheter renal denervation procedures often fail to produce complete renal denervation because of the lack of a physiological procedural endpoint., Methods: High-frequency pacing was performed in the inferior vena cava and aorta in sheep (n = 19) to identify ARG pace-capture sites. Group A (n = 5) underwent injection at the ARG pace-capture site for histological verification, group B (n = 6) underwent unilateral irrigated radiofrequency ablation of ARG pace-capture sites and assessment of renal innervation at 1 week post-procedure; and group C (n = 8) underwent ARG pacing before and 2 to 3 weeks after unilateral microwave renal denervation., Results: ARG pace-capture responses were observed at paired discrete sites above the ipsilateral renal artery eliciting a change in mean arterial blood pressure of 22.2 (interquartile range [IQR]: 15.5 to 34.3 mm Hg; p < 0.001) with concurrent ipsilateral renal arterial vasoconstriction, change in main renal artery diameter of -0.42 mm (IQR: -0.64 to -0.24 mm; p < 0.0001), and without consistent contralateral renal vasoconstriction. Sympathetic ganglionic tissue was observed at ARG pace-capture sites, and ganglion ablation led to significant ipsilateral renal denervation. Circumferential renal denervation resulted in immediate and sustained abolition of ARP pacing-induced renal vasoconstriction and significant ipsilateral renal denervation., Conclusions: Transvascular ARG pace-capture is feasible and recognized by concurrent hypertensive and ipsilateral renal arterial vasoconstrictive responses. Abolition of ARG pacing-induced vasoconstriction may indicate successful renal sympathetic denervation and serve as a physiological procedural endpoint to guide transcatheter renal denervation., (Copyright © 2019 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Aims: Trials of transcatheter renal artery denervation (RDN) have failed to show consistent antihypertensive efficacy. Procedural factors and limitations of radiofrequency ablation can lead to incomplete denervation. The aim of the study was to show that non-contact microwave catheter ablation could produce deep circumferential perivascular heating while avoiding injury to the renal artery intima and media., Methods and Results: A novel microwave catheter was designed and tested in a renal artery model consisting of layers of phantom materials embedded with a thermochromic liquid crystal sheet, colour range 50-78°C. Ablations were performed at 140 W for 180 sec and 120 W for 210 sec, delivering 25,200 J with renal arterial flow at 0.5 L/min and 0.1 L/min. Transcatheter microwave ablations 100-160 W for 180 sec were then performed in the renal arteries of five sheep. In vitro, ablations at 140 W and 0.5 L/min flow produced circumferential lesions 5.9±0.2 mm deep and 19.2±1.5 mm long with subendothelial sparing depth of 1.0±0.1 mm. In vivo, transcatheter microwave ablation was feasible with no collateral visceral thermal injury. There was histological evidence of preferential outer media and adventitial ablation., Conclusions: Transcatheter microwave ablation for RDN appears feasible and provides a heating pattern that may enable more complete denervation while sparing the renal arterial intima and media.